THIMPHU • Famed for valuing Gross National Happiness over economic growth, Bhutan is a poster child for sustainable development. But booming car sales may impact efforts to preserve its rare status as a carbon negative country - and an increase in traffic is testing the good humour of its citizens.

Bhutan has seen a more than fivefold increase in cars, buses and trucks on its roads in the past two decades, according to transport authority director-general Pemba Wangchuk, with capital Thimphu hardest hit by the vehicle influx.

Mr Phuntsho Wangdi, a media consultant, says the congestion and lack of parking make driving stressful in the tiny country where there are no traffic lights.

"I wish there were fewer cars. It wasn't like this before," he said of life in Thimpu, home to half the cars in the country.

The economy has grown 7.5 per cent each year in the past decade, according to the World Bank. Officials estimate there is one car for every seven people in Bhutan, which has a population of 750,000.

But the nation's narrow country lanes and outdated city roads can barely cope. The problem is made worse by a lack of infrastructure and poor driving etiquette - some simply leave their cars parked in the middle of the road.

"Every year, the number of cars and the number of people are increasing, and the roads have remained the same, and it's a problem for us," Mr Lhendup, a taxi driver, told Agence France-Presse.

Morning rush-hour journeys that once took five minutes now take more than half an hour. This may seem a small figure compared with the hours of gridlock faced by commuters in Manila, Jakarta and Bangkok, but it is a step change for the Bhutanese who say the situation has rapidly deteriorated in the past year.

"It's chaotic. I eat my breakfast in the car now to save time," says Ms Kuenzang Choden, who drops off her four-year-old daughter at school before heading to work.

The traffic jams are a sign of wider economic changes. Bhutan is renowned for prioritising Gross National Happiness over GDP, and has captured tourists' imagination as a tranquil, idyllic land. But there are signs of malcontent.

According to a World Bank report last year, the youth unemployment rate is high, as is rural to urban migration, which puts a strain on the resources of towns and cities. And despite its reputation as a place where well-being is prioritised, it ranked 95th out of 156 countries in this year's UN World Happiness Report.

The proliferation of the Internet and smartphones is fuelling modern desires, while car dealers are filling their showrooms with new brands from Japan and South Korea to lure buyers.

AGENCE FRANCE-PRESSE